I have been trying to understand the difference between these two terms or concepts, and I was wondering if anyone thought a good way to derive it from the Webster's Medical definition above, is to believe that mental is a "response" to something while psychological is the creation, a sparked or illogical thought process or something that pops up into the thinking without any known causation? Almost like the difference between paranoia vs hypervigilant. Paranoia is illogical, irrational with no causation while hypervigilance is triggered by something rational.

Anyone with any way to clarify easily?

To me I can also understand why it would be interchangeable to some thinkers. Even if something is deemed a faulty response from no known causation, there can be a causation - whether repressed or not fully understood.